Radiation curable composition, optical waveguide and method for formation thereof

ABSTRACT

A radiation-curable composition containing (A) hydrolyzates of hydrolyzable silane compounds represented by general formula (1): (R 1 ) p (R 2 ) q Si(X) 4-p-q  (wherein R 1  is a non-hydrolyzable organic group having 1 to 12 carbon atoms that contains fluorine atoms, R 2  is a non-hydrolyzable organic group having 1 to 12 carbon atoms (but excluding ones that contain fluorine atoms), X is a hydrolyzable group, p is an integer of 1 or 2, and q is an integer of 0 or 1) and condensates of such hydrolyzates, and (B) a photo acid generator, wherein the ratio of silanol (Si—OH) groups in the composition is 0.1 to 0.5 out of all the bonding groups on Si. With such a composition, the waveguide loss is low for light having a wavelength in a broad range from the visible region to the near infrared region, and moreover the cracking resistance, the patterning ability upon irradiation with radiation, and so on are excellent.

TECHNICAL FIELD

The present invention relates to a radiation-curable composition forproducing optical circuits used in the optical communications field, theoptical data processing field and so on, an optical waveguide using thiscomposition, and a method of forming the optical waveguide.

BACKGROUND ART

As we enter the multimedia age, there are demands to increase thecapacity and speed of data processing in optical communication systemsand computers, and transmission systems that use light as a transmissionmedium have come to be used in LANs (local area networks), FA (factoryautomation), interconnection between computers, household wiring and soon.

Optical waveguides used in such transmission systems are fundamentalconstituent elements in, for example, optical devices, optoelectronicintegrated circuits (OEICs) and optical integrated circuits (opticalICs) for realizing high-capacity data transmission of movies, movingpictures and so on, and for realizing optical computers and so on. Dueto mass demand, assiduous research is being carried out into opticalwaveguides, and in particular, high-performance and low-cost productsare demanded.

Until now, quartz optical waveguides and polymer optical waveguides havebeen known. Of these, quartz optical waveguides have better transmissionproperties than polymer optical waveguides, but a vitrifaction process(at above 1200° C.) carried out after depositing oxide fine particles,and etching treatment are required, and hence strict manufacturingconditions over a long time are required in the manufacture. On theother hand, with regard to polymer optical waveguides, a thin film caneasily be formed using a spin coating method, a dip coating method orthe like, and moreover manufacture can be carried out through alow-temperature process using reactive ion etching (RIE) orphotolithography. In particular, optical waveguides formed by usingphotolithography can be manufactured in a short time, and hence have theadvantage of being able to be formed more easily and at lower cost thanquartz optical waveguides.

As materials used for polymer optical waveguides, polysiloxanes havinghigh thermal resistance have been proposed, and by introducing phenylgroups, methyl groups, ethyl groups or the like into the polymer,control of the refractive index and improvement of cracking resistancehave been accomplished. Moreover, art, in which a polysiloxane materialknown as being heat-curable is made to be radiation-curable byintroducing radiosensitive groups therein, has also be reported (seeJapanese Patent Application Laid-open No. 2000-66051 and Japanese PatentApplication Laid-open No. 6-109936). However, the C—H bonds contained inalkyl groups such as methyl groups exhibit the second harmonic arises inthe 1.55 μm wavelength band, causing an increase in the loss in thisband. To avoid this, polysiloxanes, in which alkyl groups are not usedbut all are substituted with phenyl groups, have been reported, but thehardness of a thin film increases, and there is a tendency for a thinfilm to cause cracks during manufacture. It has been hard to attain bothloss reduction and cracking prevention.

On the other hand, an approach, in which C—H bonds contained in thepolysiloxane are substituted with C-D bonds or C—F bonds, has beenreported, but because this polysiloxane is of a heat-curable type, selfcore formation using a method such as photolithography cannot be carriedout, and hence core formation using a method such as etching has beenrequired (see Japanese Patent Application Laid-open No. 4-157402 andJapanese Patent Application Laid-open No. 2000-230052).

Furthermore, in the art of substituting C-H bonds with C-D bonds or C—Fbonds, there have been problems such as the third harmonic of the C-Dbonds again arising in the 1.55 μm wavelength band resulting indifficulty in reducing the loss, or peeling away occurring at the coreportion/clad layer or clad layer/substrate interface upon theintroduction of C—F groups.

DISCLOSURE OF THE INVENTION

As described above, the manufacture of conventional polymer opticalwaveguides is relatively easy compared with that of quartz opticalwaveguides, but there have been demands to fulfill both low transmissionloss and good cracking resistance, and make the polymer opticalwaveguide have all of various properties such as prolonged stable usewith no occurrence of cracking or peeling.

In the present invention, based on such a state of affairs, it is aimedto obtain materials for rapidly and easily forming optical waveguidesthat are excellent in terms of the above material properties.

That is, it is an object of the present invention to easily andinexpensively manufacture a material, and an optical waveguide formedusing this materials, the material and the optical waveguide having theadvantages that the waveguide loss is low for light having a wavelengthin a broad range from the visible region to the near infrared region,and moreover the cracking resistance, the thermal resistance, thepatterning ability upon irradiation with radiation, and so on areexcellent.

Moreover, it is another object of the present invention to provide anoptical waveguide formation method according to which thebefore-mentioned optical waveguide can be formed through a simpleprocess in a short time.

The present inventors carried out assiduous studies to resolve the aboveproblems, and as a result discovered that a radiation-curablecomposition, which comprises siloxane oligomers having fluorineatom-containing non-hydrolyzable organic groups and a photoacidgenerator, is extremely good as a resin for forming an opticalwaveguide, thus accomplishing the present invention.

Specifically, a radiation-curable composition of the present inventionis a radiation-curable composition which contains undermentionedcomponents (A) and (B):

(A) at least one selected from the group consisting of hydrolyzates ofhydrolyzable silane compounds represented by undermentioned generalformula (1) and condensates of such hydrolyzates(R¹)_(p)(R²)_(q)Si(X)_(4-p-q)   (1)[wherein in general formula (1), R¹ is a non-hydrolyzable organic grouphaving 1 to 12 carbon atoms that contains fluorine atoms, R² is anon-hydrolyzable organic group having 1 to 12 carbon atoms (butexcluding ones that contain fluorine atoms), X is a hydrolyzable group,p is an integer of 1 or 2, and q is an integer of 0 or 1]; and

(B) a photoacid generator;

and wherein the content of silanol (Si—OH) groups out of all the bondinggroups on Si in the composition is 10 to 50%.

If a radiation-curable composition having such a constitution is used,then an optical waveguide can be formed easily and inexpensively, whileexhibiting excellent patterning ability and so on upon irradiation withradiation. Moreover, the optical waveguide will have low waveguide lossfor light having a wavelength in a broad range from the visible regionto the near infrared region, and moreover excellent properties such ascracking resistance and thermal resistance.

Here, as component (A), for example one having therein at least onestructure selected from the group consisting of structures representedby undermentioned general formulae (2) and (3) can be used.

[In general formulae (2) and (3), R³ is a non-hydrolyzable organic grouphaving 1 to 12 carbon atoms that contains fluorine atoms, and R⁴ is anon-hydrolyzable organic group having 1 to 12 carbon atoms thatoptionally contains fluorine atoms, and may be the same as R³].

Moreover, as R¹ in general formula (1), for example a group representedby CF₃(CF₂)_(n)(CH₂)_(m) [wherein m is an integer from 0 to 5, n is aninteger from 1 to 11, and m+n is from 1 to 11] can be used.

Moreover, as component (A), one further having therein at least onestructure selected from the group consisting of structures representedby undermentioned general formulae (4) and (5) can be used.

[In general formulae (4) and (5), R⁵ is a phenyl group or a fluorinatedphenyl group, and R⁶ is a non-hydrolyzable organic group having 1 to 12carbon atoms that optionally contains fluorine atoms, and may be thesame as R⁵].

The radiation-curable composition of the present invention may beconstituted such that the amount of the photoacid generator (B) to beadded per 100 parts by weight of the component (A) is 0.01 to 15 partsby weight.

An optical waveguide formation method of the present invention is amethod of forming an optical waveguide having a lower clad layer, a coreportion formed on a part of the region of the lower clad layer, and anupper clad layer formed on the lower clad layer such as to cover thecore portion, characterized by applying on at least one selected fromthe lower clad layer, the core portion and the upper clad layer using aradiation-curable composition as described above as a material, and thenirradiating with irradiation, thus forming the optical waveguide.

An optical waveguide of the present invention is an optical waveguidehaving a lower clad layer, a core portion formed on a part of region ofthe lower clad layer, and an upper clad layer formed on the lower cladlayer such as to cover the core portion, characterized in that at leastone selected from the lower clad layer, the core portion and the upperclad layer comprises a radiation-curable composition as described above.

According to the radiation-curable composition of the present invention,an optical waveguide can be manufactured that has a low waveguide lossof not more than 0.5 dB/cm for light in a broad range of the nearinfrared region, and moreover is excellent in terms of the long-termstability of the low waveguide loss.

Moreover, according to the radiation-curable composition of the presentinvention, an optical waveguide can be manufactured that has excellenttransparency and thermal resistance, for which interfacial peeling doesnot occur and cracking inside the waveguide is not brought about, andthat has excellent shape precision.

Furthermore, according to the optical waveguide formation method of thepresent invention, an optical waveguide that has low waveguide loss andmoreover is excellent in terms of patterning ability, crackingresistance and so on can be formed through a simple process in a shorttime. Therefore optical waveguides that can be suitably used in themanufacture of optical circuits used in optical communication systemscan be provided inexpensively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing schematically an example of anoptical waveguide of the present invention, and

FIG. 2 is a flowchart showing an example of an optical waveguideformation method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Following is a more detailed description of the present invention.

[Component (A)]

Component (A) in the present invention comprises at least one selectedfrom the group consisting of hydrolyzates of hydrolyzable silanecompounds represented by undermentioned general formula (1) andcondensates of these hydrolyzates, and preferably has a silanol groupcontent of 1 to 10 mmol/g. Here, hydrolyzates of hydrolyzable silanecompounds includes not only, for example, a product obtained throughalkoxy groups being converted into silanol groups through a hydrolysisreaction, but also a partial condensate obtained through some of thesilanol groups undergoing condensation with one another or the silanolgroups undergoing condensation with alkoxy groups.(R¹)_(p)(R²)_(q)Si(X)_(4-p-q)   (1)[In general formula (1), R¹ is a non-hydrolyzable organic group having 1to 12 carbon atoms that contains fluorine atoms, R² is anon-hydrolyzable organic group having 1 to 12 carbon atoms, X is ahydrolyzable group, p is an integer of 1 or 2, and q is an integer of 0or 1.]

Component (A) can generally be obtained by heating hydrolyzable silanecompounds represented by before-mentioned general formula (1), or amixture of such hydrolyzable silane compounds and hydrolyzable silanecompounds other than those represented by general formula (1). Throughthe heating, the hydrolyzable silane compounds are hydrolyzed to form ahydrolyzate, with this hydrolyzate optionally further undergoing acondensation reaction, whereby component (A) is produced.

(1) Organic Group R¹

The organic group R¹ in general formula (1) is non-hydrolyzable organicgroup having 1 to 12 carbon atoms containing at least one fluorineatoms. Here, ‘non-hydrolyzable’ means a property of stably remaining asit is under conditions under which the hydrolyzable group X ishydrolyzed. Examples of such non-hydrolyzable organic groups includefluorinated alkyl groups and fluorinated aryl groups. Examples ofspecific fluorinated alkyl groups include trifluoromethyl groups,trifluoropropyl groups, heptadecafluorodecyl groups, tridecafluorooctylgroups, and nonafluorohexyl groups. Moreover, examples of specificfluorinated aryl groups include pentafluorophenyl groups.

Of these, fluorinated alkyl groups represented byC_(n)F_(2n+1)C_(m)H_(2m) [wherein m is an integer from 0 to 5, n is aninteger from 1 to 12, and m+n is from 1 to 12] are more preferable.Fluorinated alkyl groups, which have high fluorine contents and havelong chains, such as heptadecafluorodecyl groups, tridecafluorooctylgroups and nonafluorohexyl groups are particularly preferable.

The subscript p in general formula (1) is an integer of 1 or 2, but ispreferably 1.

(2) Organic Group R²

The organic group R² in general formula (1) is a non-hydrolyzableorganic group having 1 to 12 carbon atoms (but excluding ones thatcontain fluorine atoms). As R², a non-polymerizable organic group and apolymerizable organic group or one of these can be selected.

Here, examples of non-polymerizable organic groups include alkyl groups,aryl groups, aralkyl groups, and such groups that have been halogenatedor deuterated. These may be straight chain, branched, cyclic, or acombination thereof.

Examples of alkyl groups include a methyl group, an ethyl group, apropyl group, a butyl group, a hexyl group, a cyclohexyl group and anoctyl group. Examples of preferable halogen atoms include fluorine,chlorine, bromine and iodine.

Moreover, examples of aryl groups among the non-polymerizable organicgroups include a phenyl group, atolyl group, a xylyl group, a naphthylgroup, a biphenyl group, deuterated aryl groups, and halogenated arylgroups.

Moreover, examples of aralkyl groups include a benzyl group and aphenylethyl group.

Furthermore, as a non-polymerizable organic group, a group having astructural unit containing a hetero atom may be used. Examples of suchstructural units include ether linkages, ester linkages, sulfidelinkages and so on. Moreover, in the case of containing a hetero atom,it is preferable for the non-polymerizable organic group to benon-basic.

On the other hand, a polymerizable organic group is preferably anorganic group having one or both of a radical-polymerizable functionalgroup and a cationic-polymerizable functional group in the molecule. Byintroducing such a functional group, radical polymerization or cationicpolymerization can be made to occur, whereby the composition can becured more effectively.

Moreover, out of a radical-polymerizable functional group and acationic-polymerizable functional group in the polymerizable organicgroup, a cationic-polymerizable functional group is more preferable.This is because through the photoacid generator, not only the curingreaction for the silanol groups can be made to occur, but also thecuring reaction for the cationic-polymerizable functional group can bemade to occur at the same time.

Here, the subscript q in general formula (1) is an integer of 0 or 1,but is preferably 0.

(3) Hydrolyzable Group X

X in general formula (1) is a hydrolyzable group. Here ‘hydrolyzablegroup’ is generally a group that can be hydrolyzed to produce a silanolgroup, or a group that can form a siloxane condensate, upon heating for1 to 10 hours within a temperature range of 0 to 150° C. in the presenceof a catalyst and excess water at 1 atm.

Here, examples of the catalyst are acid catalysts and alkali catalysts.Examples of acid catalysts include monohydric and polyhydric organicacids and inorganic acids, and Lewis acids. Examples of organic acidsinclude formic acid, acetic acid and oxalic acid. Examples of Lewisacids include metallic compounds, alkoxides, carboxylates, and inorganicsalts of Ti, Zr, Al, B and so on. Examples of alkali catalysts includehydroxides of alkali metals or alkaline earth metals, amines, acidicsalts, and basic salts. The amount of the catalyst required for thehydrolysis is preferably 0.001 to 5%, more preferably 0.002 to 1%,relative to the total amount of the silane compounds.

Examples of the hydrolyzable group X include a hydrogen atom, alkoxygroups having 1 to 12 carbon atoms, halogen atoms, an amino group, andacyloxy groups.

Here, preferable examples of alkoxy groups having 1 to 12 carbon atomsinclude a methoxy group, an ethoxy group, a propoxy group, a butoxygroup, a phenoxy benzyloxy group, a methoxyethoxy group, anacetoxyethoxy group, a 2-(meth) acryloxyethoxy group, a 3-(meth)acryloxypropoxy group and a 4-(meth) acryloxybutoxy group, and alsoepoxy-group-containing alkoxy groups such as a glycidyloxy group and a2-(3,4-epoxycyclohexyl)ethoxy group, oxetanyl-group-containing alkoxygroups such as a methyl-oxetanylmethoxy group and anethyl-oxetanylmethoxy group, and 6-member ring ether groups such as anoxa-cyclohexyloxy group.

Moreover, preferable halogen atoms include fluorine, chlorine, bromineand iodine.

In the case of using a hydrolyzable silane compound containing a halogenatom as a hydrolyzable group, it is necessary to take care that thestorage stability of the composition is not reduced. That is, althoughdependent on the amount of hydrogen halide produced through thehydrolysis, it is preferable to remove this hydrogen halide through anoperation such as neutralization or distillation so that there will beno adverse effect on the storage stability of the composition.

(4) Examples of Hydrolyzable Silane Compounds Represented by GeneralFormula (1)

Examples of hydrolyzable silane compounds represented by general formula(1) include trifluoromethyltrimethoxysilane,trifluoromethyltriethoxysilane, 3,3,3-trifluoropropyltrichlorosilane,methyl-3,3,3-trifluoropropyldichlorosilane,dimethoxymethyl-3,3,3-trifluoropropylsilane,3,3,3-trifluoropropyltrimethoxysilane,3,3,3-trifluoropropylmethyldichlorosilane,3,3,4,4,5,5,5,6,6,6-nonafluorohexyltrichlorosilane,3,3,4,4,5,5,5,6,6,6-nonafluorohexylmethyldichlorosilane,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyltrichlorosilane,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyltrimethoxysilane,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyltriethoxysilane,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecylmethyldichlorosi lane,3-heptafluoroisopropoxypropyltriethoxysilane,pentafluorophenylpropyltrimethoxysilane, andpentafluorophenylpropyltrichlorosilane. Of these, for example3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyltriethoxysilane,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyltrimethoxysilane, and3,3,4,4,5,5,5,6,6,6-nonafluorohexyltrichlorosilane are preferable.

(5) Other Hydrolyzable Silane Compounds

Examples of hydrolyzable silane compounds other than the above includesilane compounds having four hydrolyzable groups such astetrachlorosilane, tetraaminosilane, tetraacetoxysilane,tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane,tetraphenoxysilane, tetrabenzyloxysilane, trimethoxysilane andtriethoxysilane; silane compounds having three hydrolyzable groups suchas methyltrichlorosilane, methyltrimethoxysilane, methyltriethoxysilane,methyltributoxysilane, ethyltrimethoxysilane, ethyltriisopropoxysilane,ethyltributoxysilane, butyltrimethoxysilane, phenyltrimethoxysilane,phenyltriethoxysilane and deuterated methyltrimethoxysilane; and silanecompounds having two hydrolyzable groups such as dimethyldichlorosilane,dimethyldiaminosilane, dimethyldiacetoxysilane, dimethyldimethoxysilane,diphenyldimethoxysilane, diphenyldiethoxysilane anddibutyldimethoxysilane.

(6) Preparation of Component (A)

There are no particular limitations on the method of heating thehydrolyzable silane compounds represented by general formula (1) toobtain component (A), so long as the silanol group content, describedlater, is not made to be too high or too low. One example of the methodis a method comprising undermentioned steps 1) to 3). Some unhydrolyzedhydrolyzable groups may remain in the hydrolyzate of the hydrolyzablesilane compounds represented by general formula (1). In this case,component (A) will be a mixture of hydrolyzable silane compounds and ahydrolyzate.

-   1) The hydrolyzable silane compounds represented by general    formula (1) and an acid catalyst are put into a vessel equipped with    a stirrer.-   2) Next, organic solvent is further put into the vessel while    adjusting the viscosity of the solution obtained, thus obtaining a    mixed solution.-   3) While stirring the mixed solution obtained in an air atmosphere    at a temperature less than the boiling point of the organic solvent    or the hydrolyzable silane compounds, water is instilled in, and    then heating and stirring are carried out for 1 to 24 hours at 0 to    150° C. During the heating and stirring, it is preferable to    concentrate the mixed solution through distillation, or replace the    organic solvents as required. Here, to adjust the refractive index    of the final cured material, the curability of the composition, the    viscosity, and so on, hydrolyzable silane compounds other than the    hydrolyzable silane compounds represented by general formula (1) can    be mixed in, whereby a siloxane oligomer is prepared. In this case,    after the hydrolyzable silane compounds other than the hydrolyzable    silane compounds represented by general formula (1) have been added    and mixing has been carried out in step 1) above, reaction can be    brought about by heating.

Silanol groups are produced in the process of preparing component (A).Depending on the preparation method, the amount of silanol groupsproduced may deviate from the range stipulated in the present invention.In this case, the waveguide loss of the optical waveguide may increase,or there may be unfavorable effects on patterning of the core portion byphotolithography or the like. It is thus preferable for the process forpreparing component (A) to follow the method described above.

(7) Preferable form of component (A)

Component (A) preferably has at least one structure selected from thegroup consisting of structures represented by undermentioned generalformulae (2) and (3).

[In general formulae (2) and (3), R³ is a non-hydrolyzable organic grouphaving 1 to 12 carbon atoms that contains fluorine atoms, and R⁴ is anon-hydrolyzable organic group having 1 to 12 carbon atoms thatoptionally contains fluorine atoms, and may be the same as R³].

If component (A) has at least one structure as described above, thenmaterial properties such as the cracking resistance of an opticalwaveguide manufactured from the radiation-curable composition of thepresent invention can be further improved.

Furthermore, R¹ in general formula (1) is preferablyCF₃(CF₂)_(n)(CH₂)_(m) [wherein m is an integer from 0 to 5, n is aninteger from 1 to 11, and m+n is from 1 to 11]. If R¹ has such astructure, the patterning ability when an optical waveguide ismanufactured through photolithography using the radiation-curablecomposition of the present invention, the cracking resistance of theoptical waveguide, the waveguide loss and so on can be further improved.

In the case that R¹ has a structure as described above, component (A)preferably further has at least one structure selected from the groupconsisting of structures represented by undermentioned general formulae(4) and (5)

[In general formulae (4) and (5), R⁵ is a phenyl group or a fluorinatedphenyl group, and R⁶ is a non-hydrolyzable organic group having 1 to 12carbon atoms that optionally contains fluorine atoms, and may be thesame as R⁵].

Examples of hydrolyzable compounds constituting a structure representedby general formula (4) or general formula (5) include compounds having aphenyl group or a fluorinated phenyl group among the examples ofhydrolyzable silane compounds represented by general formula (1) orhydrolyzable silane compounds other than those represented by generalformula (1) Out of these, phenyltrimethoxysilane, phenyltriethoxysilane,pentafluorophenyltrimethoxysilane and so on are particularly preferable.

If component (A) has a structure as described above, then the thermalresistance and the patterning ability of an optical waveguide formedusing the radiation-curable composition of the present invention can befurther improved.

[Component (B)]

Component (B) comprises a photoacid generator. Upon being irradiatedwith radiation, component (B) is decomposed, and discharges an acidicactive substance for photo-curing component (A).

Here, examples of the radiation include visible light, ultravioletradiation, infrared radiation, X-rays, an electron beam, a-rays andy-rays. From the viewpoint of the energy level being at a certain valueor more, the curing rate being high, and the irradiation apparatus beingrelatively inexpensive and small, it is preferable to use ultravioletradiation.

Examples of component (B) include onium salts having a structurerepresented by undermentioned general formula (6), and sulfonic acidderivatives having a structure represented by undermentioned generalformula (7).[R⁷ _(a)R⁸ _(b)R⁹ _(c)R¹⁰ _(d)W]^(+m)[MZ_(m+n)]^(−m)   (6)(In general formula (6), the cation is an onium ion; W is S, Se, Te, P,As, Sb, Bi, O, I, Br, Cl or —N≡N; R⁷, R⁸, R⁹ and R¹⁰ are the sameorganic group or different organic groups; each of a, b, c and d is aninteger from 0 to 3, with (a+b+c+d) being equal to the valency of W. Mis a metal or metalloid constituting the central atom of the halidecomplex [MZ_(m+n)], for example B, P, As, Sb, Fe, Sn, Bi, Al, Ca, In,Ti, Zn, Sc, V, Cr, Mn or Co. Z is a halogen atom such as F, Cl or Br, oran aryl group, m is the net charge on the halide complex ion, and n isthe valency of M.)Q_(s)-[S(═O)₂—R¹¹]_(t)   (7)[In general formula (7), Q is a monovalent or bivalent organic group,R¹¹ is a monovalent organic group having 1 to 12 carbon atoms, thesubscript s is 0 or 1, and the subscript t is 1 or 2.](1) Onium Salts

Examples of the anion [MZ_(m+n)] in general formula (6) includetetrafluoroborate (BF₄ ⁻), hexafluorophosphate (PF₆ ⁻),hexafluoroantimonate (SbF₆ ⁻), hexafluoroarsenate (AsF₆ ⁻),hexachloroantimonate (SbCl₆ ⁻), tetraphenylborate,tetrakis(trifluoromethylphenyl)borate andtetrakis(pentafluoromethylphenyl)borate.

Moreover, it is also favorable to use an anion represented by thegeneral formula [MZ_(n)OH] instead of the anion [MZ_(m+n)] in generalformula (6). Furthermore, an onium salt having another anion such as aperchlorate ion (ClO₄ ⁻), a trifluoromethanesulfonate ion (CF₃SO₄ ⁻), afluorosulfonate ion (FSO₄ ⁻), a toluenesulfonate ion, atrinitrobenzenesulfonate anion or a trinitrotoluenesulfonate anion canbe used.

Moreover, aromatic onium salts are preferable as the onium salts.Triaryl sulfonium salts, compounds represented by undermentioned generalformula (8), diaryl iodonium salts represented by undermentioned generalformula (9), and triaryl iodonium salts are particularly preferable.

[In general formula (8), each of R¹² and R¹³ represents independently ahydrogen atom or an alkyl group; R¹⁴ represents a hydroxyl group or—OR¹⁵ (wherein R¹⁵ is a monovalent organic group); a is an integer from4 to 7; and b is an integer from 1 to 7. There are no particularlimitations on the bonding positions of the substiuents on thenaphthalene ring.][R¹⁶—Ph¹—I⁺—Ph²—R¹⁷][Y⁻]  (9)[In general formula (9), each of R¹⁶ and R¹⁷ is a monovalent organicgroup, and may be the same or different, with at least one of R¹⁶ andR¹⁷ having an alkyl group having four or more carbon atoms; each of Ph¹and Ph² is an aromatic group, and may be the same or different; and Y⁻is a monovalent anion, being an anion selected from group III and groupV fluoride anions, ClO₄ ⁻, and CF₃SO₃ ⁻.

Examples of compounds represented by general formula (8) include4-hydroxy-1-naphthyltetrahydrothiophenium trifluoromethanesulfonate,4-butoxy-1-naphthyltetrahydrothiophenium trifluoromethanesulfonate,1-(4,7-dihydroxy)-naphthyltetrahydrothiopheniumtrifluoromethanesulfonate and1-(4,7-di-t-butoxy)-naphthyltetrahydrothiopheniumtrifluoromethanesulfonate.

Furthermore, examples of diaryl iodonium salts include(4-n-decyloxyphenyl)phenyliodonium hexafluoroantimonate,[4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodoniumhexafluoroantimonate,[4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodonium trifluorosulfonate,[4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodonium hexafluorophosphate,[4-(2-hydroxy-n-tetradecyloxy)phenyl]phenyliodoniumtetrakis(pentafluorophenyl)borate, bis(4-t-butylphenyl)iodoniumhexafluoroantimonate, bis(4-t-butylphenyl)iodonium hexafluorophosphate,bis(4-t-butylphenyl)iodonium trifluorosulfonate,bis(4-t-butylphenyl)iodonium tetrafluoroborate,bis(dodecylphenyl)iodonium hexafluoroantimonate,bis(dodecylphenyl)iodonium tetrafluoroborate, bis(dodecylphenyl)iodoniumhexafluorophosphate and bis(dodecylphenyl)iodoniumtrifluoromethylsulfonate. It is possible to use one such diaryl iodoniumsalt or a combination of two or more.

(2) Sulfonic Acid Derivative

Examples of the sulfonic acid derivatives represented by general formula(7) include disulfones, disulfonyl diazomethane derivatives, disulfonylmethane derivatives, sulfonyl benzoyl methane derivatives,imidosulfonates, benzoin sulfonates, 1-oxy-2-hydroxy-3-propyl alcoholsulfonates, pyrogallol trisulfonates and benzyl sulfonates.

Out of these, imidosulfonates are preferable, andtrifluoromethylsulfonate derivatives are more preferable.

There are no particular limitations on the amount of the photoacidgenerator (B), but this amount is generally 0.01 to 15 parts by weightper 100 parts by weight of component (A). If the amount of the photoacidgenerator is less than 0.1 parts by weight, then there may be a tendencyfor the photo-curability to drop, and hence it may not be possible toobtain a sufficient curing rate. On the other hand, if the amount of thephotoacid generator exceeds 15 parts by weight, then there may be atendency for the weather resistance and thermal resistance of the curedmaterial to drop.

From the viewpoint of making the balance between the photo-curabilityand the weather resistance and so on of the cured material obtained yetbetter, the amount of the photoacid generator as component (B) ispreferably made to be a value within a range of 0.1 to 10 parts byweight per 100 parts by weight of component (A).

[Component (C)]

The radiation-curable composition of the present invention can have goodstorage stability and a suitable viscosity, and can form an opticalwaveguide having a uniform thickness by being mixed in an organicsolvent (C).

Examples of the organic solvent (C) include ether type organic solvents,ester type organic solvents, ketone type organic solvents, hydrocarbontype organic solvents, and alcohol type organic solvents. In general, itis preferable to use an organic solvent that has a boiling point underatmosphere pressure within a range of 50 to 200° C., and which candissolve the components of the composition uniformly.

Examples of such organic solvents include aliphatic hydrocarbon typesolvents, aromatic hydrocarbon type solvents, monoalcohol type solvents,polyalcohol type solvents, ketone type solvents, ether type solvents,ester type solvents, nitrogen-containing solvents, sulfur-containingsolvents and so on can be used. One of these organic solvents can beused alone, or two or more can be used in combination.

Out of these organic solvents (C), alcohols and ketones are preferable.This is because the storage stability of the composition can be furtherimproved.

Moreover, an example of particularly preferable organic solvent is atleast one compound selected from the group consisting of propyleneglycol monomethyl ether, ethyl lactate, methyl isobutyl ketone, methylamyl ketone, toluene, xylene, and methanol.

Moreover, the type of the organic solvent (C) is preferably selectedwhile considering the method of applying the composition. For example,because a thin film having a uniform thickness can easily be obtained,it is preferable to use the spin coating method. As an organic solventused in this case, it is preferable to use a glycol ether such asethylene glycol monoethyl ether or propylene glycol monomethyl ether; anethylene glycol alkyl ether acetate such as ethyl cellosolve acetate,propylene glycol methyl ether acetate or propylene glycol ethyl etheracetate, an ester such as ethyl lactate or ethyl 2-hydroxypropionate; adiethylene glycol derivative such as diethylene glycol monomethyl ether,diethylene glycol dimethyl ether or diethylene glycol ethyl methylether; a ketone such as methyl isobutyl ketone, 2-heptanone,cyclohexanone or methyl amyl ketone, or the like. It is particularlypreferable to use ethyl cellosolve acetate, propylene glycol methylether acetate, ethyl lactate, methyl isobutyl ketone or methyl amylketone.

The amount of component (C) is 1 to 300 parts by weight, preferably 2 to200 parts by weight, per 100 parts by weight of component (A). If thisamount is within a range of 1 to 300 parts by weight, then the storagestability of the composition can be improved, and moreover thecomposition can be given a suitable viscosity, and hence an opticalwaveguide having a uniform thickness can be formed.

There are no particular limitations on the method of adding the organicsolvent (C). For example, the organic solvent (C) may be added whencomponent (A) is being manufactured, or may be added when component (A)and component (B) are being mixed together.

[Silanol Group Content in Composition]

The content of silanol groups out of all the bonding groups on Si in theradiation-curable composition of the present invention must be 10 to 50%(preferably 20 to 40%). If the content of silanol groups deviates fromthis range, then it may not be possible to obtain patterning in thedesired shape upon carrying out alkaline developing, or the waveguideloss of the formed optical waveguide may be increased.

[Other Components]

It is favorable to further blend in acid diffusion controlling agents,reactive diluents, radical generators (photopolymerization initiators),photosensitizers, metal alkoxides, inorganic fine particles, dehydratingagents, leveling agents, polymerization inhibitors, polymerizationinitiation auxiliaries, wettability improvers, surfactants,plasticizers, ultraviolet absorbers, antioxidants, antistatic agents,silane coupling agents, macromolecular additives and so on, providedthat the objects and effects of the present invention are not impaired.

(D) Acid Diffusion Controlling Agent

An acid diffusion controlling agent, which is component (D), is definedas a compound capable of controlling diffusion of acidic activesubstance, which generates from the photoacid generator upon irradiationwith light, through the coating film, thus suppressing the curingreaction in unexposed regions. To distinguish an acid diffusioncontrolling agent, which is component (D), from a photoacid generator,an acid diffusion controlling agent is defined as a compound not havingan acid generating function.

By adding such an acid diffusion controlling agent, the photo-curablecomposition can be cured effectively, and the pattern precision can beimproved.

As the type of the acid diffusion controlling agent, which is component(D), a nitrogen-containing organic compound, the basicity of which doesnot change upon exposure to light or heat treatment during the filmformation process, is preferable.

Examples of such nitrogen-containing organic compounds include, forexample, compounds represented by undermentioned general formula (10).NR¹⁸R¹⁹R²⁰   (10)[In general formula (10), each of R¹⁸, R¹⁹ and R²⁰ representsindependently a hydrogen atom, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted aryl group, or a substituted orunsubstituted aralkyl group.]

Moreover, examples of other nitrogen-containing organic compoundsinclude diamino compounds having two nitrogen atoms in the samemolecule, diamino polymers having three or more nitrogen atoms, and alsoamide group-containing compounds, urea compounds, andnitrogen-containing heterocyclic compounds.

Examples of nitrogen-containing organic compounds includemonoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine,n-nonylamine and n-decylamine; dialkylamines such as di-n-butylamine,di-n-pentylamine, di-n-hexylamine, di-n-heptylamine, di-n-octylamine,di-n-nonylamine and di-n-decylamine; trialkylamines such astriethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-pentylamine,tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamineand tri-n-decylamine; aromatic amines such as aniline, N-methylaniline,N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline,4-nitroaniline, diphenylamine, triphenylamine and 1-naphthylamine; andalkanolamines such as ethanolamine, diethanolamine and triethanolamine.

One acid diffusion controlling agent can be used alone, or two or morecan be used mixed together.

The amount of the acid diffusion controlling agent (D) is preferablywithin a range of 0.001 to 15 parts by weight per 100 parts by weight ofcomponent (A).

The reasons for this are as follows. If the amount of the acid diffusioncontrolling agent is less than 0.001 parts by weight, then depending onthe process conditions, the pattern shape and the dimensionalreproducibility of the optical waveguide may become poor. On the otherhand, if the amount of the acid diffusion controlling agent exceeds 15parts by weight, then the photo-curability of component (A) may drop.

It is thus preferable to make the amount of the acid diffusioncontrolling agent be a value within a range of 0.001 to 10 parts byweight, more preferably 0.005 to 5 parts by weight, per 100 parts byweight of component (A).

Radiation-curable compositions of the present invention can be used as alower layer composition, a core composition and an upper layercomposition for forming the lower clad layer, the core portion and theupper clad layer constituting an optical waveguide.

As the lower layer composition, the core composition and the upper layercomposition, different resin compositions can be used, this being suchthat the relationship between the refractive indexes of these partsfinally obtained satisfies the conditions required for the opticalwaveguide. It is preferable for the lower layer composition and theupper layer composition to be the same resin composition, because theformation of the optical waveguide and so on becomes easier.

By selecting the type of component (A) in the radiation-curablecomposition of the present invention, an optical waveguide comprising acore portion and lower and upper clad layers having different refractiveindexes can easily be formed. It is thus preferable to select two ormore resin compositions such that the refractive index differencetherebetween is suitable, and then, for example, use a resin compositionfor which a high refractive index is obtained as the core composition,and use a resin composition for which a lower refractive index than thatof the core composition is obtained as the lower layer composition andthe upper layer composition.

Moreover, the viscosity of a radiation-curable composition of thepresent invention is preferably 5 to 5,000 mPa.s, more preferably 10 to1,000 mPa.s, at 25° C. If the viscosity exceeds 5,000 mPa.s, then it maybe difficult to form a uniform coating film. The viscosity of the resincomposition can be adjusted by regulating the amount of a reactivediluent and an organic solvent.

Next, a description will be given of a method of forming an opticalwaveguide using the radiation-curable composition of the presentinvention. This method is constituted primarily from a lower clad layerformation step, a core portion formation step, and an upper clad layerformation step. Following is a detailed description, with reference toFIG. 1. FIG. 1 is a sectional view showing schematically an example ofan optical waveguide of the present invention.

In the following description, a radiation-curable composition of thepresent invention is used for each of the lower clad layer 2, the coreportion 4 and the upper clad layer 6.

However, for example, a radiation-curable composition of the presentinvention may be used for only the core portion 4. In this case, apublicly known optical waveguide material such as quartz glass can beused for the lower clad layer 2 and the upper clad layer 6.

In the optical waveguide having the above constitution, there are noparticular limitations on the thicknesses of the lower clad layer 2, theupper clad layer 6 and the core portion 4, but for example it ispreferable to make the thickness of the lower clad layer 2 be a valuewithin a range of 3 to 50 μm, the thickness of the core portion 4 be avalue within a range of 3 to 20 μm, and the thickness of the upper cladlayer 6 be a value within a range of 3 to 50 μm.

Moreover, there are no particular limitations on the width of the coreportion 4 in the direction perpendicular to the light waveguidingdirection, but it is preferable, for example, to make this width have avalue within a range of 1 to 50 μm.

Next, a description will be given of an optical waveguide formationmethod of the present invention. FIG. 2 is a flowchart showing anexample of an optical waveguide formation method of the presentinvention.

In the present invention, the optical waveguide is formed through steps(a) to (e) as shown in FIG. 2. That is, each of the lower clad layer 2,the core portion 4 and the upper clad layer 6 (not shown in FIG. 2—seeFIG. 1) is preferably formed by applying a photo-curable composition foroptical waveguide formation for forming that layer, and thenphoto-curing.

In the following formation example, description is given assuming thatthe lower clad layer 2, the core portion 4 and the upper clad layer 6are formed respectively from a lower layer composition, a corecomposition and an upper layer composition. These compositions arephoto-curable compositions for optical waveguide formation from whichcured materials of different refractive indices are obtained aftercuring.

(1) Preparation of Substrate

First, as shown in FIG. 2(a), a substrate 1 having a flat surface isprepared. There are no particular limitations on the type of thesubstrate 1, but for example a silicon substrate, a glass substrate orthe like can be used.

(2) Lower Clad Layer Formation Step

This is a step of forming the lower clad layer 2 on the surface of theprepared substrate 1. Specifically, as shown in FIG. 2(b), the lowerlayer composition is applied onto the surface of the substrate 1, anddried or prebaked to form a lower layer thin film. The lower layer thinfilm is then cured by being irradiated with light, whereby the lowerclad layer 2 can be formed.

There are no particular limitations on the light for forming the corelayer and the clad layers, but in general, light from the ultraviolet tovisible region of wavelength 200 to 450 nm, preferably light containingultraviolet radiation of wavelength 365 nm is used. The irradiation atwavelength 200 to 450 nm is carried out such that the intensity is 1 to1000 mW/cm², and the irradiation dose is 0.01 to 5000 mJ/cm², preferably0.1 to 1000 mJ/cm², thus carrying out exposure.

Here, as the type of the irradiated light, visible light, ultravioletradiation, infrared radiation, X-rays, α-rays, β-rays, γ-rays and so oncan be used, but due to the industrial versatility of the light source,a wavelength of 200 to 400 nm is preferable, and irradiation containingultraviolet radiation of wavelength 365 nm is particularly preferable.Moreover, it is possible to use, for example, an irradiation apparatus,in which light from either or both of a lamp light source thatirradiates a wide area simultaneously such as a high-pressure mercurylamp, a low-pressure mercury lamp, a metal halide lamp or an excimerlamp, and a laser light source that emits light as pulses or continuousemission, is converged using mirrors, lenses or optical fibers.

In the case of forming the optical waveguide using convergent light, theexposure can be carried out to give the shape of the optical waveguideby moving either the convergent light or the irradiated object. Of thebefore-mentioned light sources, a light source having high ultravioletradiation intensity at 365 nm is preferable. For example, ahigh-pressure mercury lamp is preferable as a lamp light source, and anargon laser is preferable as a laser light source.

In the step of forming the lower clad layer 2, it is preferable toirradiate the whole of the thin film with light, thus curing the wholeof the thin film.

Here, as the method of applying the lower layer composition, a methodsuch as a spin coating method, a dipping method, a spraying method, abar coating method, a roll coating method, a curtain coating method, agravure printing method, a silk screen method, or an ink jet method canbe used. Of these, it is particularly preferable to use the spin coatingmethod, because a lower layer thin film of particularly uniformthickness can be obtained.

Moreover, to make the Theological properties of the lower layercomposition suitably match the application method, it is possible toblend in additives other than surface-tension reducing agents asrequired.

Moreover, it is preferable to prebake the lower layer thin filmcomprising the lower layer composition at 50 to 200° C. after theapplication.

The application method, the rheological property improving method and soon in the lower clad layer formation step can also be used in the coreportion formation step and the upper clad layer formation step describedbelow.

Moreover, after the exposure, to cure the whole of the coating filmsufficiently, it is preferable to further carry out heating treatment(hereinafter referred to as ‘post-baking’). The heating conditions willvary according to the composition of the photo-curable composition foroptical waveguide formation, the types of additives, and so on, but itis generally preferable to make the heating time be, for example, 5minutes to 72 hours, and the heating temperature be at 30 to 400° C.,preferably 50 to 300° C.

The irradiation dose and type of the light, the irradiation apparatusand so on in the lower clad layer formation step can also be used in thecore portion formation step and the upper clad layer formation stepdescribed below.

(3) Formation of Core Portion

Next, as shown in FIG. 2(c), the core composition is applied onto thelower clad layer 2, and dried or further prebaked to form a core thinfilm 3.

After that, as shown in FIG. 2(d), radiation 5 is preferably irradiatedonto the upper surface of the core thin film 3 following a prescribedpattern, for example via a photomask 7 having a prescribed line pattern.

As a result, only parts irradiated with the light are cured, and henceby developing and removing the remaining uncured parts using adeveloping solution, as shown in FIG. 2(e), a core portion 4 comprisinga patterned cured film can be formed on the lower clad layer 2.

Here, the method of irradiating with light following a prescribedpattern is not limited to a method using a photomask comprising regionsthrough which the light can pass and regions through which the lightcannot pass. Examples of other methods include the following methods ato c.

-   a. A method using means for electrooptically forming a mask image    comprising regions through which the light can pass and regions    through which the light cannot pass following a prescribed pattern,    using a similar principle to a liquid crystal display apparatus.-   b. A method in which a light-guiding member comprising a bundle of    many optical fibers is used, and irradiation with light is carried    out via the optical fibers in accordance with a prescribed pattern    in the light-guiding member.-   c. A method in which laser light, or convergent light obtained using    a converging optical system such as a lens or a mirror, is    irradiated onto the photo-curable composition while being scanned.

After the exposure, to promote the curing of the exposed regions, it ispreferable to carry out heating treatment (hereinafter referred to as‘PEB’). The heating conditions will vary according to the composition ofthe photo-curable composition for optical waveguide formation, the typesof additives, and so on, but the temperature is generally 30 to 200° C.,preferably 50 to 150° C.

On the other hand, before the exposure, merely by leaving the coatingfilm comprising the photo-curable composition for optical waveguideformation for 1 to 10 hours at room temperature, the shape of the coreportion can be made to be semicircular. In the case that one wishes toobtain a semicircular core portion, it is preferable to leave forseveral hours at room temperature before the exposure in this way.

The thin film that has been selectively cured by exposing with lightfollowing a prescribed pattern as described above can be developedutilizing the difference in solubility between the cured portions andthe uncured portions. After the patterned exposure, it is thus possibleto remove the uncured portions while leaving behind the cured portions,and as a result form the core portion.

Here, as the developing solution, it is possible to use a solutionobtained by diluting a basic substance such as sodium hydroxide,potassium hydroxide, sodium carbonate, sodium silicate, sodiummetasilicate, ammonia, ethylamine, n-propylamine, diethylamine,di-n-propylamine, triethylamine, methyldiethylamine, ethanolamine,N-methylethanolamine, N,N-dimethylethanolamine, triethanolamine,tetramethylammonium hydroxide, tetraethylammonium hydroxide,tetrabutylammonium hydroxide, choline, pyrrole, piperidine,1,8-diazabicyclo[5.4.0]-7-undecene or 1,5-diazabicyclo[4.3.0]-5-nonenewith a solvent such as water, methanol, ethanol, propyl alcohol,butanol, octanol, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, N-methylpyrrolidone, formamide, N,N-dimethylformamideor N,N-dimethylacetoamide.

The concentration of the basic substance in the developing solution isgenerally made to be a value within a range of 0.05 to 25 wt %,preferably 0.1 to 3.0 wt %.

Moreover, the developing time is generally 30 to 600 seconds. As thedeveloping method, a publicly known method such as a liquid mountingmethod, a dipping method, or a showering developing method can be used.

In the case of using an organic solvent as the developing solution, blowdrying is carried out. In the case of using an alkaline aqueoussolution, washing in running water is carried out for, for example, 30to 90 seconds, and then blow drying is carried out using compressed air,compressed nitrogen or the like, whereby moisture is removed from thesurface, and hence a patterned coating film can be formed.

Next, to further cure the patterned portions, post-baking is carriedout, for example, at a temperature of 30 to 400° C. for 5 to 60 minutesusing a heating apparatus such as a hot plate or an oven, whereby acured core portion is formed.

For the core composition, it is preferable to use an aminopolysiloxanehaving higher amino group content than in the lower layer composition orthe upper layer composition.

By adopting such a constitution, the pattern precision of the coreportion can be further improved, and on the other hand for the lowerlayer composition and the upper layer composition, excellent storagestability can be obtained, and moreover curing can be carried outsufficiently with a relatively low irradiation dose.

(4) Formation of Upper Clad Layer

Next, the upper layer composition is applied onto the surface of thelower clad layer 2 on which the core portion 4 has been formed, and isdried or prebaked to form an upper layer thin film. The upper layer thinfilm is then cured by being irradiated with light, whereby an upper cladlayer 6 as shown in FIG. 1 can be formed.

Moreover, the upper clad layer 6 obtained through the irradiation ispreferably subjected to post-baking as described earlier as required. Bycarrying out post-baking, an upper clad layer having excellent thermalresistance and hardness can be obtained.

Moreover, with regard to the optical waveguide, it is necessary to makethe refractive index of the core portion 4 be greater than therefractive index of the lower clad layer 2 and the upper clad layer 6.To obtain excellent waveguiding properties, it is preferable to make therefractive index of the core portion 4 be a value within a range of1.450 to 1.650, and the refractive index of the lower clad layer 2 andthe upper clad layer 6 be a value within a range of 1.400 to 1.648, forlight of wavelength 1300 to 1600 nm.

Moreover, it is preferable to set the refractive index of the coreportion 4 while considering the refractive index of the lower clad layer2 and the upper clad layer 6. It is particularly preferable to make therefractive index of the core portion 4 be a value 0.002 to 0.5 greaterthan the value of the refractive index of the lower clad layer 2 and theupper clad layer 6.

EXAMPLES

Following is a description of examples of the present invention.

In the following, the present invention is described more concretelythrough Examples. However, the present invention is not limited to theseExamples.

[Preparation of Component (A)]

Synthesis Example 1

Phenyltrimethoxysilane (30.79 g),3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyl-triethoxy-silan e (22.64g), tetraethoxysilane (4.62 g), 1-methoxy-2-propanol (29.93 g), andoxalic acid (0.04 g) were added into a flask equipped with a stirrer anda reflux tube, and after stirring, the solution was heated to atemperature of 60° C. Next, distilled water (11.98 g) was instilled in,and after the instillation had been completed, the solution was stirredat 120° C. for 6 hours. Ultimately, a 1-methoxy-2-propanol solution of acomponent (A) having the solid content adjusted to 65 wt % was obtained.This shall be referred to as ‘siloxane oligomer solution 1’.

Synthesis Example 2

Phenyltrimethoxysilane (30.56 g),3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyl-triethoxy-silan e(18.15g), tetraethoxysilane (9.88g),methyl-n-amylketone (27.72 g), andoxalic acid (0.04 g) were added into a flask equipped with a stirrer anda reflux tube, and after stirring, the solution was heated to atemperature of 60° C. Next, distilled water (13.66 g) was instilled in,and after the instillation had been completed, the solution was stirredat 120° C. for 6 hours. Ultimately, a methyl-n-amyl ketone solution,which is component (A), having the solid content adjusted to 70 wt % wasobtained. This shall be referred to as ‘siloxane oligomer solution 2’.

Synthesis Example 3

Methyltrimethoxysilane (2.97 g), phenyltrimethoxysilane (29.01 g),3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyl-triethoxy-silan e (25.64g), 1-methoxy-2-propanol (31.00 g), and oxalic acid (0.04 g) were addedinto a flask equipped with a stirrer and a reflux tube, and afterstirring, the solution was heated to a temperature of 60° C. Next,distilled water (11.35 g) was instilled in, and after the instillationhad been completed, the solution was stirred at 120° C. for 6 hours.Ultimately, a 1-methoxy-2-propanol solution of component (A) having thesolid content adjusted to 70 wt % was obtained. This shall be referredto as ‘siloxane oligomer solution 3’.

Comparative Synthesis Example 1

Phenyltrimethoxysilane (30.79 g),3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorodecyltriethoxysilane (22.64g),tetraethoxysilane (4.62g), 1-methoxy-2-propanol (29.93 g), and oxalicacid (0.04 g) were added into a flask equipped with a stirrer and areflux tube, and after stirring, the solution was heated to atemperature of 60° C. Next, distilled water (11.98 g) was instilled in,and after the instillation had been completed, the solution was stirredat 120° C. for 6 hours. After that, the 1-methoxy-2-propanol wasremoved, and the viscous liquid thus obtained was further subjected tovacuum drying. This shall be referred to as ‘siloxane oligomer 4’.

Comparative Synthesis Example 2

Pentafluorophenylethyltrichlorosilane (236.9 g) and(3,3,3-trifluoropropyl)trichlorosilane (231.5 g) were dissolved in 1liter of tetrahydrofuran that had been subjected to dehydrationtreatment, and water (92.9 g) was instilled in slowly such that theliquid temperature did not rise. Next, while stirring the reactionliquid, sodium hydrogencarbonate (433.4 g) was added therein. After thegeneration of carbon dioxide had finished, stirring was continued for afurther 1 hour. Next, the reaction liquid was filtered, and thetetrahydrofuran was distilled off from the filtrate using a rotaryevaporator, whereupon a transparent colorless viscous liquid wasobtained. This liquid was further subjected to vacuum drying, thusobtaining ‘siloxane oligomer 5’.

Comparative Synthesis Example 3

Methyltrimethoxysilane (32.27 g), phenyltrimethoxysilane (24.41 g),1-methoxy-2-propanol (23.85 g), and oxalic acid (0.03 g) were added intoa flask equipped with a stirrer and a reflux tube, and after stirring,the solution was heated to a temperature of 60° C. Next, distilled water(19.44 g) was instilled in, and after the instillation had beencompleted, the solution was stirred at 120° C. for 6 hours. Ultimately,a 1-methoxy-2-propanol solution having a solid content adjusted to 70 wt% was obtained. This shall be referred to as ‘siloxane oligomer solution6’.

Comparative Synthesis Example 4

A copolymer of methyl methacrylate and3-methacryloxypropyltrimethoxysilane (solid concentration: 27wt %,diluted with methoxypropanol) (28.16 g), methyltrimethoxysilane (36.42g), phenyltrimethoxysilane (20.37 g), and oxalic acid (0.04 g) wereadded into a flask equipped with a stirrer and a reflux tube, and afterstirring, the solution was heated to a temperature of 60° C. Next,distilled water (15.01 g) was instilled in, and after the instillationhad been completed, the solution was stirred at 60° C. for 6 hours.Ultimately, a 1-methoxy-2-propanol solution having a solid contentadjusted to 70 wt % was obtained. This shall be referred to as ‘siloxaneoligomer solution 7’

[Preparation of Radiation-Curable Compositions]

0.32 g of 1-(4,7-di-t-butoxy)-naphthyltetrahydrothiopheniumtrifluoromethanesulfonate as a photoacid generator, 0.03 g oftri-n-octylamine, and 7.09 g of 1-methoxy-2-propanol were added to 92.56g (solid component plus organic solvent) of siloxane oligomer solution1, and mixing to homogeneity was carried out, thus obtaining a‘Composition 1’ having the solid concentration adjusted to 65 wt %.

‘Composition 2’ to ‘Composition 8’ as shown in Table 1 were thenprepared in a similar way to ‘Composition 1’. TABLE 1 CompositionComposition Composition Composition Composition Composition Composition(Units: g) 1 2 3 4 5 6 7 A Siloxane oligomer solution 1 92.6 Siloxaneoligomer solution 2 92.6 Siloxane oligomer solution 3 92.8 A′ Siloxaneoligomer 4 64.8 Siloxane oligomer 5 64.8 Siloxane oligomer solution 685.2 Siloxane oligomer solution 7 92.8 B 1-(4,7-di-t-butoxy)- 0.32 0.320.32 0.32 0.32 0.06 naphthyltetrahydrothiopheniumtrifluoromethanesulfonate SP172 (made by Asahi Denka) 0.06 C1-methoxy-2-propanol¹⁾ 39.5 35.0 34.9 34.9 40.0 35.0 Methyl-n-amylketone²⁾ 34.9 D Trioctylamine 0.03 0.03 0.03 0.03 Amount of component(A) 60.2 64.8 65.0 Amount of siloxane oligomer other 64.8 64.8 59.6 65.0than (A) Content of silanol groups out of all 29 28 30 5 4 23 25 bondinggroups on Si (%)¹⁾Amount of 1-methoxy-2-propanol includes amount contained in siloxaneoligomer solution.²⁾Amount of methyl-n-amyl ketone is amount contained in siloxaneoligomer solution.

Example 1

Composition 3 was applied onto the surface of a silicon substrate usinga spin coater, drying was carried out for 10 minutes at 120° C., andthen irradiation with ultraviolet radiation of wavelength 365 nm andintensity 6 mW/cm² was carried out for 3 minutes using an exposingapparatus (a photo-aligner made by Canon). Heating was then furthercarried out for 1 hour at 200° C., thus forming a lower clad layer ofthickness 9 μm. The refractive index of this lower clad layer to lightof wavelength 1550 nm was 1.439.

Next, composition 1 was applied onto the lower clad layer using a spincoater, drying was carried out for 5 minutes at 100° C., and then usinga photomask having an optical waveguide pattern of width 9 μm formedtherein, exposure was carried out by irradiating with ultravioletradiation of wavelength 365 nm and intensity 6 mW/cm² for 1 minute usingan exposing apparatus. After that, the substrate was heated for 1 minuteat 100° C., and was then immersed in a developing solution comprising a5 % tetramethylammonium hydroxide (TMAH) aqueous solution to dissolvethe unexposed parts, and was then washed with water. After that,irradiation with ultraviolet radiation was carried out for 3 minutes,and then heating was carried out for 1 hour at 200° C., thus forming acore portion of thickness 9 μm. The refractive index of the obtainedcore portion to light of wavelength 1550 nm was 1.445.

Radiation-curable composition 3 was further applied using a spin coateronto the upper surface of the lower clad layer having the core portionthereon, drying was carried out for 10 minutes at 120° C., and thenirradiation with ultraviolet radiation of wavelength 365 nm andintensity 6 mW/cm² was carried out for 10 minutes. Heating was thenfurther carried out for 1 hour at 250° C., thus forming an upper cladlayer of thickness 9 μm, whereby an optical waveguide was formed. Therefractive index of the formed upper clad layer to light of wavelength1550 nm was 1.439.

For Example 2 and Comparative Examples 1, 2 and 3, an optical waveguidewas again manufactured in a similar way to Example 1, and evaluation wascarried out. The evaluation results are shown in Table 2. TABLE 2Comparative Comparative Comparative Example 1 Example 2 Example 1Example 2 Example 3 Materials Under-cladding Composition CompositionComposition Composition Composition 3 3 7 7 7 Core CompositionComposition Composition Composition Composition 1 2 4 5 6 Over-claddingComposition Composition Composition Composition Composition 3 3 7 7 7Properties Patterning ability ◯ ◯ X (*) X (*) ◯ Waveguide loss 1310 nm0.3 0.3 — — 0.4 [dB/cm] 1550 nm 0.4 0.4 — — 1.0 Interfacial peeling ◯ ◯— — ◯ Cracking resistance ◯ ◯ — — X Long-term reliability ◯ ◯ — — X(*) Patterning was not possible.[Measurement of Silanol Content]

Each composition was diluted with deuterated chloroform, which is asolvent for NMR measurement, and the silanol content was measured bySi-NMR. Specifically, for the plurality of silane components havingdifferent substituents or bonding groups appearing from −120 ppm to −60ppm, the peaks were separated by curve fitting, and the molarpercentages of the components were calculated from the area ratios ofthe peaks. Then, multiplying by the number of silanol groups in eachcomponent obtained, the proportion (%) of silanol groups out of all thebonding groups on Si was calculated.

An example calculation is as follows: Mol % Number of silanol groupsPeak 1: R—Si(OH)₃ a 3 Peak 2: R—Si(OH)₂(OSi) b 2 Peak 3: R—Si(OH)(OSi)₂c 1 Peak 4: R—Si(OSi)₃ d 0[Patterning Ability]

Each manufactured waveguide was cleaved to reveal an end face, and thecore shape (width, height) was measured using an optical microscope. Thecase of being within ±0.5 m from the design values (width 9 μm, height 9μm) was taken as ‘◯’, and the case that this was not so, or the shapewas rectangular or trapezoidal, or the core could not be patterned wastaken as ‘X’.

[Waveguide Loss]

Light of wavelength 1310 nm or 1550 nm was inputted from one end of thewaveguide, and the quantity of light emerging from the other end wasmeasured using a power meter (MT9810A actinometer made by Anritsu) todetermine the loss [dB]. The waveguide loss [dB/cm] was obtained bycleaving the waveguide, measuring the loss at each length, plotting theloss against the length, and calculating the waveguide loss [dB/cm] fromthe gradient of the graph (cut-back method).

[Interfacial Peeling]

An end face obtained by cleaving the manufactured waveguide was observedusing a scanning electron microscope (SEM), thus measuring whether ornot there was peeling away between the substrate and the lower cladlayer, the lower clad layer and the core portion, the core portion andthe upper clad layer, or the lower clad layer and the upper clad layer.Furthermore, it was observed whether or not there was peeling away onthe core line using an optical microscope from above the waveguide. Thecase that peeling was not observed in either case was taken as ‘◯‘, andthe case that peeling was observed in either case was taken as ‘X’.

[Cracking Resistance]

The obtained waveguide was heated for 1 hour at 300° C., and was allowedto cool naturally, and then it was observed over the whole of thewaveguide using an optical microscope whether or not cracking hadoccurred; the case that cracking was not observed was taken as ‘◯’, andthe case that cracking was observed in either the core portion or theclad layers was taken as ‘X’.

[Long-Term Reliability]

The obtained waveguide was left for 2000 hours under conditions of atemperature of 85° C. and a relative humidity of 85%, and was then leftfor 24 hours at a temperature of 25° C. and a relative humidity of 50%.The transmission loss was measured, and the waveguide loss wascalculated. The case that the waveguide loss was not more than 0.5 dB/cmat both a wavelength of 1310 nm and a wavelength of 1550 nm was taken as‘◯’, and the case that was not so was taken as ‘X’.

1. A radiation-curable composition comprising components (A) and (B):(A) at least one member selected from the group consisting ofhydrolyzates of hydrolyzable silane compounds represented by generalformula (1) and condensates of said hydrolyzates(R¹)_(p)(R²)_(q)Si(X)_(4-p-q)   (1) wherein, in general formula (1), R¹is a non-hydrolyzable organic group having 1 to 12 carbon atoms thatcontains fluorine atoms, R² is a non-hydrolyzable organic group having 1to 12 carbon atoms (but excluding ones that contain fluorine atoms), Xis a hydrolyzable group, p is an integer of 1 or 2, and q is an integerof 0 or 1]; and (B) a photoacid generator; wherein a content of silanol(Si—OH) groups out of all the bonding groups on Si in the composition is10 to 50%.
 2. The radiation-curable composition according to claim 1,wherein said component (A) has at least one structure selected from thegroup consisting of structures represented by general formulae (2) and(3)

[wherein, in general formulae (2) and (3), R³ is a non-hydrolyzableorganic group having 1 to 12 carbon atoms that contains fluorine atoms,and R⁴ is a non-hydrolyzable organic group having 1 to 12 carbon atomsthat optionally contains fluorine atoms, and may be the same as R³]. 3.The radiation-curable composition according to claim 2, wherein R¹ ingeneral formula (1) is CF₃(CF₂)_(n)(CH₂)_(m) and wherein m is an integerfrom 0 to 5, n is an integer from 1 to 11, and m+n is from 1 to 11]. 4.The radiation-curable composition according to claim 3, wherein saidcomponent (A) further has at least one structure selected from the groupconsisting of structures represented by general formulae (4) and (5)

[wherein, in general formulae (4) and (5), R⁵ is a phenyl group or afluorinated phenyl group, and R⁶ is a non-hydrolyzable organic grouphaving 1 to 12 carbon atoms that optionally contains fluorine atoms, andmay be the same as R⁵].
 5. The radiation-curable composition accordingto claim 1, wherein the amount added of said photoacid generator (B),per 100 parts by weight of said component (A), is 0.01 to 15 parts byweight.
 6. A method of forming an optical waveguide comprising a lowerclad layer, a core portion formed on a part of the region of said lowerclad layer, and an upper clad layer formed on said lower clad layer,such as to cover said core portion, the method comprising, by applyingon at least one member selected from said lower clad layer, said coreportion or said upper clad layer, a radiation-curable compositionaccording to claim 1, as a material, and irradiating with irradiation,thus forming the optical waveguide.
 7. An optical waveguide comprising alower clad layer, a core portion formed on a part of the region of saidlower clad layer, and an upper clad layer formed on said lower cladlayer, such as to cover said core portion, and wherein at least onemember, selected from said lower clad layer, said core portion or saidupper clad layer, comprises a radiation-curable composition according toclaim
 1. 8. The radiation-curable composition according to claim 2,wherein the amount of said photoacid generator (B), per 100 parts byweight of said component (A), is 0.01 to 15 parts by weight.
 9. Theradiation-curable composition according to claim 3, wherein the amountof said photoacid generator (B), per 100 parts by weight of saidcomponent (A), is 0.01 to 15 parts by weight.
 10. The radiation-curablecomposition according to claim 4, wherein the amount of said photoacidgenerator (B), per 100 parts by weight of said component (A), is 0.01 to15 parts by weight.
 11. A method of forming an optical waveguidecomprising a lower clad layer, a core portion formed on a part of theregion of said lower clad layer, and an upper clad layer formed on saidlower clad layer, such as to cover said core portion, the methodcomprising, applying, on at least one member selected from said lowerclad layer, said core portion or said upper clad layer, aradiation-curable composition according to claim 2, as a material, andirradiating with irradiation, thus forming the optical waveguide.
 12. Amethod of forming an optical waveguide comprising a lower clad layer, acore portion formed on a part of the region of said lower clad layer,and an upper clad layer formed on said lower clad layer, such as tocover said core portion, the method comprising, applying, on at leastone member selected from said lower clad layer, said core portion orsaid upper clad layer, a radiation-curable composition according toclaim 3, as a material, and irradiating with irradiation, thus formingthe optical waveguide.
 13. A method of forming an optical waveguidecomprising a lower clad layer, a core portion formed on a part of theregion of said lower clad layer, and an upper clad layer formed on saidlower clad layer, such as to cover said core portion, the methodcomprising, applying, on at least one member selected from said lowerclad layer, said core portion or said upper clad layer, aradiation-curable composition according to claim 4, as a material, andirradiating with irradiation, thus forming the optical waveguide.
 14. Amethod of forming an optical waveguide comprising a lower clad layer, acore portion formed on a part of the region of said lower clad layer,and an upper clad layer formed on said lower clad layer, such as tocover said core portion, the method comprising, applying, on at leastone member selected from said lower clad layer, said core portion orsaid upper clad layer, a radiation-curable composition according toclaim 5, as a material, and irradiating with irradiation, thus formingthe optical waveguide.
 15. An optical waveguide comprising a lower cladlayer, a core portion formed on a part of the region of said lower cladlayer, and an upper clad layer formed on said lower clad layer, such asto cover said core portion, and wherein at least one member, selectedfrom said lower clad layer, said core portion or said upper clad layer,comprises a radiation-curable composition according to claim
 2. 16. Anoptical waveguide comprising a lower clad layer, a core portion formedon a part of the region of said lower clad layer, and an upper cladlayer formed on said lower clad layer, such as to cover said coreportion, and wherein at least one member, selected from said lower cladlayer, said core portion or said upper clad layer, comprises aradiation-curable composition according to claim
 3. 17. An opticalwaveguide comprising a lower clad layer, a core portion formed on a partof the region of said lower clad layer, and an upper clad layer formedon said lower clad layer, such as to cover said core portion, andwherein at least one member, selected from said lower clad layer, saidcore portion or said upper clad layer, comprises a radiation-curablecomposition according to claim
 4. 18. An optical waveguide comprising alower clad layer, a core portion formed on a part of the region of saidlower clad layer, and an upper clad layer formed on said lower cladlayer, such as to cover said core portion, and wherein at least onemember, selected from said lower clad layer, said core portion or saidupper clad layer, comprises a radiation-curable composition according toclaim 5.